1. Field of the Invention
This invention relates to a routing design method for working out a routing design for a system in package (SiP), a routing design apparatus and a recording medium that stores a routing design program.
2. Description of the Related Art
Recently, a SiP having a plurality of LSI chips stacked on a package board is developed. For example, in a SiP having a lower chip mounted on the package board and an upper chip mounted on the lower chip with a re-distribution layer disposed therebetween, the upper chip is electrically connected to the package board via bonding wires. Specifically, a signal input/output terminal of the upper chip is formed to extend from a bump of the upper chip to a solder ball of the package board via a re-distribution layer route, bonding pad, bonding wire, bonding finger and package board route (for example, see Jpn. Pat. KOKAI Publication No. 2008-123341).
Algorithms suitable for coping with routing problems that are used for a routing portion (re-distribution layer routing portion) extending from the bump of the upper chip to the bonding pad and a routing portion (package board routing portion) extending from the bonding finger to the solder ball are different from each other. Therefore, in the prior art technique, the re-distribution layer routing portion and package board routing portion are individually optimized at the time of routing design of each routing portion.
However, if the re-distribution layer routing portion and package board routing portion are individually optimized, allocation of nets to the bonding wire is determined according to the state of a routing portion that is previously routed, and therefore, allocation for a routing portion that is later routed may become unfavorable. This causes a problem that the routing efficiency of the routing portion later routed is lowered, for example, the number of design rule check (DRC) errors increases.